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Codeine

Nicknames: AC/DC, Coties, schoolboy, DFs, lean, purp, purple drank
Last reviewed: October 2026

Pharmacology

Codeine is selective for the µ-opioid receptor, but with a much weaker affinity than morphine. At least some of the analgesic properties of codeine have been speculated to come from its conversion into morphine by the CYP2D6 liver enzyme, although the exact mechanism of analgesic action is less well understood than the more potent members of the opiate family. Around 10% of the population will experience less analgesia from codeine as a result of variations in CYP2D6 activity (Crews et al. 2011).

Codeine is absorbed from the gastrointestinal tract with maximum plasma concentration occurring 60 minutes post administration. Codeine is absorbed quickly from the GI tract and its first pass through the liver results in very little loss of the drug. This contrasts with morphine in which over 90% of the drug is metabolised in the first pass through the liver resulting in a considerable loss of potency when administered orally. This is why codeine is a common opiate in the relief of pain, the ease of oral administration.

Taking codeine in combination with other depressants can increase the risk of fatal overdose. Drinking alcohol or taking benzodiazepines, Z-drugs, or gabapentinoids alongside codeine can cause severe sedation and slow down breathing to dangerous levels. Naloxone is an opioid antagonist which can reverse the effects of opioid overdose: to find out more about how naloxone works, head to our Naloxone page.

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